18 research outputs found
Instability of supersymmetric microstate geometries
We investigate the classical stability of supersymmetric, asymptotically
flat, microstate geometries with five non-compact dimensions. Such geometries
admit an "evanescent ergosurface": a timelike hypersurface of infinite
redshift. On such a surface, there are null geodesics with zero energy relative
to infinity. These geodesics are stably trapped in the potential well near the
ergosurface. We present a heuristic argument indicating that this feature is
likely to lead to a nonlinear instability of these solutions. We argue that the
precursor of such an instability can be seen in the behaviour of linear
perturbations: nonlinear stability would require that all linear perturbations
decay sufficiently rapidly but the stable trapping implies that some linear
perturbation decay very slowly. We study this in detail for the most symmetric
microstate geometries. By constructing quasinormal modes of these geometries we
show that generic linear perturbations decay slower than any inverse power of
time.This work was supported by European Research Council grant ERC-2011-StG279363-HiDGR.This is the final version of the article. It first appeared from Springer via https://doi.org/10.1007/JHEP10(2016)03
Comments on black holes in bubbling spacetimes
In five-dimensional minimal supergravity, there are spherical black holes
with nontrivial topology outside the horizon which have the same conserved
charges at infinity as the BMPV solution. We show that some of these black
holes have greater entropy than the BMPV solution. These spacetimes are all
asymptotically flat, stationary, and supersymmetric. We also show that there is
a limit in which the black hole shrinks to zero size and the solution becomes a
nonsingular "bubbling" geometry. Thus, these solutions provide explicit
analytic examples of placing black holes inside solitons.Comment: 17 pages, 5 figures; v2: references adde
Sustained Antibiotic-Eluting Intra-Ocular Lenses: A New Approach
Currently, infections following cataract surgery are not as effectively managed with antibiotic eye drops, which suffer from poor bioavailability of drug and low patient compliance. The ideal solution, which can help to overcome the issue of drug wastage and poor bioavailabilty, as well as the need for frequent applications (patient inconvenience), is a drug-eluting intraocular lens (IOL). We describe a novel approach to such a drug-eluting lens by using a peripheral IOL attachment as a drug depot to deliver antibiotics, Levofloxacin (LFX) or Moxifloxacin (MFX). In this work, drug was entrapped within a fully-degradable polymer, poly(L-lactide-co-ɛ-caprolactone) (PLC). The effects of drug loading and solvent type on drug release and film morphology were investigated using cast films. The study clearly demonstrated that a slower-evaporating solvent tetrahydrofuran (THF) resulted in a better surface morphology, as well as lower initial burst compared to dichloromethane (DCM), and hence, was better suited to developing a drug-eluting attachment with sustained release of drug. When attachments were fabricated with drugs at high loading percentages (20% and 25% in polymer), significant burst was observed compared to films: this is attributed to the higher surface-to-volume ratio of the attachments. When the levofloxacin (LFX) loading percentage was decreased to 3% and 5%, the attachments presented lower burst and sustained release with therapeutic efficacy. This work has demonstrated the potential of using an IOL attachment as a more efficacious anti-infective option compared to daily eye drops